Fermion mediated pairing in the Ruderman-Kittel-Kasuya-Yosida to Efimov transition regime

TL;DR

This paper investigates the transition between RKKY interactions and Efimov physics in a Bose-Fermi mixture, revealing fermion-mediated resonances that connect condensed matter and nuclear physics phenomena.

Contribution

It provides experimental evidence of the RKKY-Efimov transition in a strongly interacting Bose-Fermi mixture near a Feshbach resonance.

Findings

Identification of fermion-mediated scattering resonance

Observation of Efimov resonance in thermal regime

Connection between many-body and few-body physics

Abstract

The Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction and Efimov physics are two distinct quantum phenomena in condensed matter and nuclear physics, respectively. The RKKY interaction describes correlations between impurities mediated by an electron gas, while Efimov physics describes universal bound states of three particles with resonant interactions. Recently, both effects have been observed in Bose-Fermi mixtures in the weak and resonant interaction regimes, respectively. Intriguing conjectures exist to elucidate how the two phenomena meet in the transition regime where the mixture is strongly interacting. In this work, we explore the RKKY-Efimov transition in a mixture of bosonic Cs-133 and fermionic Li-6 near a tunable interspecies Feshbach resonance. From dispersion and relaxation measurements, we find that the transition is highlighted by a fermion-mediated scattering resonance between Cs atoms and a weaker resonance on Li atoms. These resonances represent reactive scattering of Cs and Li atoms in the many-body regime, which reduces to an Efimov resonance in the thermal gas regime. Our observation demonstrates the intriguing interplay of two-, three-, and many-body physics in an Bose-Fermi mixture that connects condensed matter physics, nuclear physics and quantum many-body chemistry.